1. Field of the Invention
The present invention concerns gas discharge lamps, particularly those which emit short wavelength light usable in instrumentation.
2. Description of the Relevant Art
A gas discharge lamp encases electrodes and gas within an envelope which is transparent or translucent to light. When an electrical discharge path is established between the electrodes through ionized gas, then the ionized gas emits light radiation of a known frequency. This light radiation passes through the envelope and is .[.visable.]. .Iadd.visible .Iaddend.or elsewise usable as a light source.
In the prior art a low-cost gas discharge lamp is produced with a light-transparent envelope, or dome, which is normally made of quartz. The envelope is filled with a gas, normally mercury vapor, and sealed to a base. Gas-tight electrical connection is made through this base to two electrodes within the chamber of the lamp envelope. These two electrodes may be, in some prior art lamps, separated by a partition which is within the quartz envelope and between the electrodes. This partition may be, in some cases, simply the central dividing wall of a double-bore glass tube from which the gas discharge lamp is fabricated. The partition defines, in combination with the envelope, a bore about each of the electrodes. The partition terminates and the bores join at that end of the domed envelope which is opposite to the base of the lamp. An electrical discharge path is established through the gas starting from one electrode, proceeding along the bore of this electrode then across the dome of the tube and then along the bore of the other electrode to electrically connect with the other electrode. Such a prior art gas discharge lamp is generally known as a double bore discharge lamp; a bore existing in the region of each electrode upon each side of the substantially centrally located partition. Such a double bore gas discharge lamp with a quartz envelope is inexpensive and easy to fabricate, and the partition imparts structural strength.
It is also known in the prior art to create an alternative gas discharge lamp producing an alternative electrical discharge path producing an alternative light illumination. This alternative gas discharge lamp is particularly directed to producing one or more regions of high illumination intensity, appearing as bright spots. In this alternative gas discharge lamp each electrode is sheathed in a tube, typically called a capillary tube. The tubes sheathing each electrode are fairly tight about the electrode and are substantially spaced parallel. No envelope partition exists within this type of gas discharge lamp. The electrical discharge path proceeds from the electrode within a capillary tube, along the bore of this tube, across the dome of the gas discharge lamp to the opening to the other capillary tube, along the bore of this tube, and finally terminates at the other electrode. This discharge path provides a particularly concentrated current density, and a resultantly bright region of ionized gas and light output, at the opening to the bore of each capillary tube. Two bright spots thus appear. This type of prior art gas discharge tube is sometimes called a single bore gas discharge lamp and sometimes called a capillary-tube gas discharge lamp.
Problems, and difficulties, exist in the manufacture of this alternative prior art capillary-tube gas discharge lamp. Special jigs must be used to hold the capillary tubes in position during manufacture. The capillary tubes are not always well or reliably aligned.
Furthermore, the quartz envelope which is commonly used for the double-bore gas discharge lamp or for the capillary tube, single bore, gas discharge lamp is not transparent to short wavelength light. Known frequency sources of short wavelength light are desired in many applications, particularly including instrumentation applications. Consequently, at least the single bore, or capillary, gas discharge lamp has been modified in the prior art to suitably emit short wavelength light radiation. This modification consists of making the .Iadd.upper window portion of the .Iaddend.envelope of a special material.Iadd., such as magnesium fluoride, .Iaddend.which is substantially transparent to short wavelength light, .[.normally of boro silicate.]. .Iadd.which window is normally fused to borosilicate .Iaddend.material .Iadd.forming the remaining portion of the envelope.Iaddend.. This .[.boro silicate.]. .Iadd.borosilicate .Iaddend.envelope is difficult and expensive to manufacture.
Moreover, a .[.boro silicate.]. .Iadd.borosilicate .Iaddend.envelope will not seal reliably to electrodes of molybdenum of tungsten which are desired for their high current carrying capacity. Consequently within the prior art capillary-tube gas discharge lamps for short wavelength light emission electrodes of KOVAR material are used. This material, which is required in order to seal gas tight to .[.boro silicate.]. .Iadd.borosilicate.Iaddend., is inferior in current carrying capacity to tungsten or molybdenum electrodes.
Correspondingly, it is desired that some way should be found to more economically manufacture a gas discharge lamp producing short wavelength light particularly suitable for instrumentation. This lamp should simultaneously .[.possesses.]. .Iadd.possess .Iaddend.high physical strength and be supportive of high currents for producing high illumination levels.